This invention relates to a method for the separation of bismuth from chloride solutions containing high concentrations of other metals. More particularly, this invention relates to a method of separating bismuth from complex chloride solutions containing other metals using as precipitating agents hexamminecobalt (III) and hexamminechromium (III) salts.
Bismuth is a rare metal obtained as a by-product in copper, lead, and zinc production. The metal or its compounds are useful in low-melting alloys, thermoelectric devices, castings, magents, catalysts, medicines, and cosmetics.
Bismuth is commonly recovered from smelter flue dusts, anode slimes, and lead bullion by pyrometallurgical and hydrometallurgical techniques. With hydrometallurgical techniques, bismuth is the major component in solution and is readily recovered by hydrolytic precipitation, sulfide or carbonate precipitation, cementation, or electrolysis.
Recovery of bismuth by known techniques from the pregnant leach solutions of hydrometallurgical processes, however, is technically or economically infeasible. The pregnant solutions often contain high concentrations of Fe, Cu, Pb, or Zn, and low concentrations of bismuth, and the pH is usually maintained below 3.0 to prevent hydrolysis of solubilized metals in major concentrations. Therefore, separation of bismuth via hydrolytic precipitation of bismuth from leach solutions of hydrometallurgical processes by dilution with water or by precipitation by neutralization with bases is not feasible.
Leaching of Cu concentrates by ferrous chloride/oxygen solutions produces solutions having a pH of 1 to 2 containing CuCl.sub.2 and FeCl.sub.2 and solubilized bismuth. Although bismuth in such solutions could be precipitated as BiOCl by raising the pH to 3 or 4, this procedure fails to produce a pure Bi product because Cu(II) and Fe(II) react to form Cu(I) and Fe(III) oxide precipitate at pH above 2.5 with consumption of base. Sulfide precipitation of bismuth also fails in the presence of Cu(II) or Fe(III) because these metal ions oxidize sulfides.
Cementation or electrolysis of Bi in the presence of Cu or Fe(III) cannot be done because any reagent capable of reducing Bi(III) to Bi metal will reduce Fe(III) to Fe(II) and Cu(II) to Cu(I) or Cu metal.
It is an object of the invention to provide a method for the separation of bismuth from solutions containing same which avoids the aforementioned problems. In particular it is an object of the present invention to recover bismuth from solutions which contain as well high concentrations of other metal components that interfere with prior art bismuth recovery techniques.